This invention relates to the field of direct drive mechanical stages for precision motion control. More specifically, it relates to small footprint linear motor driven positioning stages and multi-axis mechanical positioners useful in the alignment of optic fibers.
Optic fibers are being used more and more for the transfer of information due to the large bandwidth and insensitivity to certain types of electromagnetic interference. Optic fibers are transparent glass fibers through which light waves encoded with information are passed. The fibers themselves are often less than 100 nm in diameter. Typically, they are enclosed in a protective coating. The fibers are not infinitely long and, therefore, it is necessary to align and bond fibers together. The alignment must be very precise, that is, the centers of the fibers must be aligned in order to minimize power loss across a bonded joint. Not only must fibers be joined end to end, fibers must be connected to tiny components, such as transmitters, amplifiers, and receivers. This process is referred to in the industry as pig-tailing.
In order to position fibers for fiber-to-fiber bonding or pig-tailing automatically, mechanical positioning stages and multi-axis mechanical positioners with extremely high resolution and repeatability are required. Very often, the bonding and pig-tailing take place in clean rooms. The expense of building and maintaining clean rooms is directly related to the volume of the room. Hence, miniaturization of the mechanical positioning stages for use in optic fiber alignment is extremely critical.
The extent of the motion required to execute the final fiber alignment is on the order of 100""s of microns. This is due to the relatively small size of the fiber itself. Core diameters vary from 200 microns for multi-mode fibers down to 9 microns for single-mode fibers. The relative small distances required to align the fibers are dwarfed by the size of even the smallest positioning stages now in successful use.
The smallest possible alignment stage volume is currently attainable with stages driven by piezoelectric crystals mounted in structures known in the art as flexures. These tools have limited maximum travel. This lack of travel has necessitated the use of a combination of a coarse positioning stage (millimeters of travel) with a piezoelectric flexure stage if a movement greater than about 200 microns is required for the initial alignment and/or transferring to a position for final alignment. One marketed multi-axis mechanical positioner for fiber alignment uses piezoelectric flexures for the X and Y axes and a ball screw driven stage for the vertical axis. The ball screw drive is a mechanical contact driven device subject to wear. Also, the footprint is 4 inches by 7 inches. Yet another marketed multi-axis mechanical positioner for this application is entirely ball screw driven having a footprint of about 4.5 inches by 4 inches. It is, of course, inherently subject to the problems of mechanical wear and the backlash associated with ball screw driven stages. Perhaps the most successful multi-axis mechanical positioner now being marketed is entirely driven by noncontact permanent magnet linear motors. Due to the design of the motors and other factors, the size of the footprint is still a relatively large 5 inches by 7 inches.
In addition to the need for a small footprint, it is especially desirable that as much of the multi-axis mechanical positioner as possible be located below the table surface holding the remaining apparatus needed for effecting the fiber alignment. The auxiliary apparatus may comprise fixtures for holding optic fibers and or tiny parts to which the fibers are attached and robotic apparatus for picking and placing fibers and tiny components. The auxiliary apparatus may also be optical devices for robotic vision systems to aid in alignment. Hence, it is desirable that the multi-axis mechanical positioner and all the wiring associated with it be recessed below the top surface of the table.
Footprint and travel ranges are not the only criteria for selection of a positioning stage for fiber alignment applications. Speed, accuracy, repeatability, and positioning stability are also very critical.
It is an advantage, according to the present invention, to provide a small footprint linear motor driven positioning stage that has a combination of a small footprint, a long travel range, high speed, high accuracy, high repeatability, and high position stability that make it a superior choice for fiber alignment applications.
It is a further advantage, according to the present invention, to provide multi-axis mechanical positioners based upon the small footprint positioning stage.
It is yet a further advantage, according to the present invention, that the substantial portions of the multi-axis mechanical positioner can be recessed below the surface of the table to which it is directly secured without the need for suspending a platform below the surface of the table.
Briefly, according to the present invention, there is provided a small footprint mechanical positioning stage capable of operating in two perpendicular orientations. The stage comprises a base plate comprising a flat bed, a short platform rising from the bed near one edge of the bed, and a short perpendicular wall rising from the bed near an opposite edge of the bed. The stage further comprises a carriage plate comprising a flat table plate and a short side wall pendent from the table plate near one edge of the table plate.
A first linear bearing is positioned between the base plate and the carriage plate fixed to the platform rising from the flat bed and a second linear bearing is positioned between the base plate and the carriage plate fixed to the wall rising from the flat bed and the wall pendent from the carriage plate. The first linear bearing provides maximum support in the direction perpendicular to the flat bed and the table plate and the second linear bearing provides maximum support in the direction between edges of the flat bed and table plate parallel to the direction of travel of the stage. This enables the use of the stage in two perpendicular orientations.
A direct drive brushless linear motor comprises an armature winding fixed to the base plate having a magnetic focusing plate between the armature winding and the base plate and a rare earth magnet track fixed to the table plate having a magnetic focusing plate between the magnet track and the table plate. A linear encoder reader is fixed to the flat bed and an encoder scale is fixed to the table plate.
The first and second linear bearings, the linear motor, and the encoder scale are all oriented parallel to the direction of travel of the positioning stage. The distance between the table plate and the base plate is just sufficient to accommodate the linear motor, the linear encoder, and the linear bearings.
Two of the above-described stages can be handily combined into a small footprint X-Y mechanical positioner. A second small footprint mechanical positioning stage is arranged with its base plate affixed to the carriage plate of the first small footprint mechanical stage. Further, a small footprint X-Y-Z mechanical positioner can be assembled from two of the stages above described and a vertical left stage mounted on the carriage plate of the second small footprint mechanical stage.
A small footprint X-Y-Z-Theta mechanical positioner can be assembled from three of the above-described small footprint mechanical positioning stages by using two of the stages arranged on a foundation plate mounted with base plates thereof attached to edges of the foundation plate. Flanges may be secured to the upper edges of the two stages enabling them to be secured in a table opening extending downwardly from the table surface. A carriage plate parallel to the foundation plate bridges the carriage plates of the two small footprint mechanical positioning stages. The third small footprint mechanical positioning stage is mounted on the carriage plate oriented for travel perpendicular to the travel of the first and second small footprint mechanical positioning stages. A vertical lift stage is mounted on the carriage plate of the third small footprint mechanical positioning stage, and a rotary stage is mounted on the vertical lift stage. A five-axis small footprint mechanical positioner may be assembled by attaching a goniometric cradle mount to the rotary stage and a six-axis mechanical positioner may be assembled by attaching a double goniometric cradle to the rotary stage. This construction minimizes the vertical height of the four-, five-, and six-axis stages. It is facilitated by the fact that the above-described small axis linear stages are capable of two perpendicular orientations.